I am currently using the script 'plex for kodi', which has become very popular.
I notice that the simkl script is not triggered as it should when using this script and the result is that no ratings are posted to simkl. The Trakt script is triggered correctly, so it should be possible to fix.
The plex for kodi script gives you a separate gui from within kodi and things are probably handled differently which probably is the cause.
The log does not say anything as it is not triggered.